Abstract
Metals of Ni or Cu joined to Si3N4 ceramics with Ag- or Ni-brazing filler (Ag-Cu-Ti and Ni-Cu-Ti) were thermally cycled in vacuum between room temperature and the temperatures of 573, 723 and 873 K, and then the surface distortion and fracture strength of the joints were measured using scanning acoustic microscopy and a four-point bending test.
In the case of the RT-573 K cycling there was little change in the joints, whereas Ni and Cu metals swelled at both of the RT-723 K and RT-873 K cycles and Ni swelling was much larger than that of Cu due to Ni plate sliding at the Ag-rich layer formed within the brazing filler. The fracture strength decreased significantly after the thermal-cyclings, because of the crack formation near the ceramic/filler interface.
In the case of the Si3N4/Ni joint the Ni metal shrank at the early stages of the thermal cycling and then it tended to swell with the crack formation near ceramic-filler interfaces. The integrity of ceramic/metal joints could be controlled by the mechanical properties of metal components at the elevated temperatures.
